Interesting decision on ICOM’s part to choose MiniDin8 connector for packet and leave 3 pins on it unused while there is a de-facto industry standard for MiniDin6 packet socket. That plus the fact that there is a well established use for MiniDin8 as a serial CAT connector. 
The audio cable for Digirig will look like this:
MiniDin8 pin 1 (DATA IN) → 3.5mm TRRS ring 1 (RIG_AFIN)
MiniDin8 pin 2 (GND) → 3.5mm TRRS sleeve (GND)
MiniDin8 pin 3 (PTT P) → 3.5mm TRRS ring 2 (RIG_PTT)
MiniDin8 pin 5 (DATA OUT) → 3.5mm TRRS tip (RIG_AFOUT)
ID-800H INSTRUCTION MANUAL.pdf (36.6 KB)